The present invention relates to a method and apparatus for forming a web of material into a plurality of individual rolls. More particularly, the present invention relates to such a method and apparatus which insures that lightweight stretchable web materials are evenly wound into precise rolls with a minimum amount of material distortion.
Relatively thin sheet materials such as film, foil, paper, laminate and cloth are typically manufactured in the form of wide, long webs, which may measure, for example, six feet in width by one thousand feet in length. Each web is usually wound about an elongate cylindrical supply core for transport and storage. The manufacture of consumer products from such webs, for example rolls of adhesive tape, usually involves the use of an apparatus known as a slitter-rewinder. Examples of this type of apparatus are currently manufactured by Voorwood Company, 2350 Barney Street, Anderson, Calif. 96007 and Arrow Converting Equipment, Inc., Law Drive, Fairfield, N.J. 07006.
Known slitter-rewinder apparatus typically include an upright frame which supports a pair of powered takeup rollers and a supply roller or chuck for rotatably supporting the supply core and supply roll. During the rewinding operation, the web is guided by idler rollers from around the supply core past a series of slitting blades. The resulting strips of web material are rewound about a plurality of corresponding product cores on opposite ones of the takeup rollers in alternating fashion to give the necessary clearance between adjacent product rolls during their formation.
Heretofore, every slitter-rewinder apparatus known to me has utilized the powered takeup rollers for pulling the web material from around the supply core. This latter core has not been directly powered but has been rotated only through the pulling action supplied by the takeup rollers. An adjustable drag brake, usually of the disc type, has been utilized to prevent over-spinning of the supply roll. The disc brake has also been used to attempt to maintain the tension necessary for proper slitting and rewinding.
Known slitter-rewinder apparatus are used as follows. The product cores are slid over the takeup rollers with spacers splined to the takeup rollers positioned between adjacent product cores. Pneumatic means are utilized to compress the product cores endwise against the spacers with a predetermined amount of pressure. At the start of the rewinding operation, the supply core is initially fully braked to prevent rotation thereof. The takeup rollers are rotated within the stationary product cores which are held in position because of their attachment to the non-moving strips of the web material. The brake on the supply core is then gradually released manually, or automatically by means of a sensing device known as a dancer roll tension control. Eventually the friction between the product cores and the spacers is sufficient to cause the product cores to rotate and rewind the strips. The speed of rotation of the product cores increases as the brake is further released.
Heretofore with the slitter-rewinder apparatuses described above it has been difficult to precisely control the tension of the web portion extending between the supply and product cores to insure proper slitting and rewinding. This is especially true in the case of lightweight stretchable web materials such as acetate. Generally a relatively great amount of pulling force and resulting web tension are required to unwind the web from around the supply core. The amount of pulling force required increases as the diameter of the web around the supply core decreases and the resulting leverage is reduced. If the disc brake is released too quickly to compensate for the increased pulling forces required, then over-spinning occurs and the strips of web material weave laterally. The resulting product rolls are not uniformally edge aligned, but instead have a telescoping or other undesirable configuration. If the brake is released too slowly, then the web tension is too great and the material stretches. The resulting product rolls then have a slightly smaller intermediate diameter than edge diameter. When the strips are unrolled from these product rolls they are distorted and frequently have undulating side edges. This problem is particularly acute where the gauge or the thickness of the web varies across the width thereof. Regions called gauge bands, which extend lengthwise of the web and are of relatively greater thickness, will form high spots on the product roll when tightly rewound.